Cerebral haemorrhagic contusions are a type of intracerebral haemorrhage and are common in the setting of significant head injury.
They are usually characterised on CT as hyperdense foci in the frontal lobes adjacent to the floor of the anterior cranial fossa and in the temporal poles.
Contusions, by definition, result from head trauma and are thus seen more frequently in young males. Typical causes include motor vehicle accidents (MVA) or situations in which the head strikes the pavement.
Most contusions represent the brain coming to a sudden stop against the inner surface of the skull (contrecoup) accentuated by the natural contours of the skull (see below).
- intraventricular haemorrhage in ~2.5% 7
Cerebral contusions can occur anywhere, but have a predilection for certain locations, as a result of the direction of the head strike and the intrinsic shape of the skull cavity.
Typically cortical contusions become more apparent on follow-up imaging due to further bleed or surrounding oedema. Hence on follow-up CT scans in the first couple of days after trauma, one may detect the increase in number and size of the lesions but the patient may not show any clinical deterioration.
Furthermore, the appearance of contusions will vary according to when they are imaged. Typically they mature over some weeks, initially appearing as merely haemorrhagic foci, followed by the development of surrounding oedema, before gradually fading away leaving behind more or less distinct areas of gliosis.
In most hospitals, CT is usually the first and often the only investigation used to assess cerebral contusions. Sensitivity to detect intracerebral haemorrhage on CT scans is virtually 100%.
Hounsfield units (HU) of blood are dependent on protein concentration (i.e. haemoglobin) and haematocrit.
With a haematocrit of 45% the density of whole blood is ~56 HU while the grey matter is 37-41 HU and white matter is 30-34 HU. So blood should be hyperdense in comparison to grey or white matter.
Of note, in anaemic patients (i.e. haemoglobin < 8-10 g/dL) blood may appear isodense in an acute bleeding.
Contusions vary in size and can appear as small petechial foci of hyperdensity/haemorrhages involving the grey matter and subcortical white matter or large cortical/subcortical bleed.
Signal behaviour is strongly dependent on sequence and time since the bleeding started.
Practical pearls and pitfalls
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- 7. Castillo M. Neuroradiology Companion: Methods, Guidelines, and Imaging Fundamentals. LWW. ISBN:1451111754. Read it at Google Books - Find it at Amazon